A power semiconductor module provided with an insulated gate bipolar transistor with a sensing function (referred to simply as an IGBT hereinafter), which is a type of power semiconductor device, a free-wheeling diode (referred to as an FWD simply hereinafter), which is connected in parallel to the IGBT so as to cause a current to flow in the direction opposite to the current flowing to the IGBT, and a temperature detection diode that detects temperatures in a module are widely used in power conversion devices such as an inverter, a chopper circuit, etc. Note that an IGBT, an FWD and a temperature detection diode that constitute a power semiconductor module are formed on one or a plurality of semiconductor chips.
In order to control a power semiconductor module as described above, a method is generally known in which an output current (specifically, a current flowing to the sensing area of an IGBT) is detected so as to detect a presence or absence of a short circuit in order to prevent the power semiconductor module from breaking and to suppress a temperature increase in the power semiconductor module by detecting the temperature in the module (see Patent Document 2).
FIG. 1 shows a configuration of a conventional drive control method of a power semiconductor module. In FIG. 1, a gate drive unit 51 provided on the high voltage side applies a prescribed drive voltage to the gate of an IGBT 61 so as to make the IGBT operate, and receives, in a gate drive unit 51, signal output from a short-circuit protection unit 52 and an undervoltage protection unit 53 serving as protection units that respond to abnormality in a semiconductor module (which will be described later), so as to protect the IGBT 61. The undervoltage protection unit 53 protects the gate drive unit 51 by detecting a decrease indirect current voltage (not shown) applied to the gate drive unit 51 so as to compensate for the shortage of voltage. Also, the short-circuit protection unit 52 operates as described below so as to protect the gate drive unit 51 and also protects a power semiconductor module 60.
In other words, the IGBT 61 provided on the high voltage side uses the sensing function of the IGBT to detect the principal current that flows to the IGBT, detects by using the short-circuit protection unit 52 whether or not the detected principal current has exceeded a predetermined overcurrent protection level continuously for a prescribed period of time, determines, when detecting an overcurrent, the overcurrent and prevents the IGBT from breaking due to the overcurrent by interrupting the switch control of the IGBT 61 to be conducted by the gate drive unit 51. Meanwhile, when an overcurrent has been detected, the short-circuit protection unit 52 transmits an alarm signal to a control unit (not shown) from an alarm signal output terminal provided on the low voltage side via a photocoupler (PC2) 72 provided between the high voltage side and the low voltage side. Usually, a latch period is set for an alarm signal so that an alarm state is maintained during the latch period, and the alarm is responded to before the expiration of the alarm latch period (for example, cancellation of the alarm etc. if possible).
The temperature of a board including a power semiconductor module is detected by using a temperature detection element (for example, a temperature detection diode) 63 provided on the board (semiconductor board (chip), a printed circuit board, etc.) that mounts the power semiconductor module 60, the detected temperature is converted into a digital signal (which will be explained later) by using a temperature information generating unit 54, and the digitized temperature information is transmitted to a control unit (not shown) from a temperature information output terminal provided on the low voltage side via a photocoupler (PC3) 73 provided between the high voltage side and the low voltage side.
In the above, the gate drive unit 51, the short-circuit protection unit 52, the undervoltage protection unit 53 and the temperature information generating unit 54 constitute a gate drive control block 50, and usually this gate drive control block 50 is realized in an integrated form.
The control unit (not shown) provided on the low voltage side includes for example a central processing unit (CPU) or a logic IC or a system LSI including a logic IC and a CPU, etc., receives an alarm signal and temperature information transmitted from the high voltage side via the photocoupler (PC2) 72 and the photocoupler (PC3) 73, and instructs via the drive signal input terminal and a photocoupler (PC1) 71 the gate drive unit 51 to analyze their contents and conduct prescribed processes. When for example the control unit (not shown) has determined from the analysis of an alarm state that it is necessary to protect the power semiconductor module 60 from an overcurrent, the gate drive unit 51 is instructed via the drive signal input terminal and the photocoupler (PC1) 71 to halt the on/off operation of the IGBT 61 and to fix it to off.
When the obtained temperature information has exceeded a prescribed threshold, the control unit (not shown) transmits to the gate drive unit 51 an instruction to decrease overloads via the drive signal input terminal and the photocoupler (PC1) 71 similarly to the above, so that the operation of decreasing overloads is conducted in order to decrease the temperature of the power semiconductor module 60. The outline of a system that conducts this control is disclosed by for example Patent Document 2 below.
FIG. 2 shows signal waveforms related to temperature information and an alarm signal in a conventional drive control method of a power semiconductor module. The temperature information in FIG. 2 is a PWM signal whose duty ratio of pulse ON width is determined by the temperature detected by the temperature detection element 63, and is transmitted to the control unit (not shown) on the low voltage side from the temperature information generating unit 54 via the photocoupler (PC3) 73. Also, the alarm signal in FIG. 2 represents a high level state in a normal operation without alarm output, represents a waveform that includes a binary state so that a low level state can be represented in a protection operation with alarm output, and is transmitted from the short-circuit protection unit 52 to the control unit (not shown) on the low voltage side via the photocoupler (PC2) 72.
FIG. 3 shows the setting of a duty ratio of the above pulse ON width with respect to temperature information in the conventional drive control method of a power semiconductor module.
FIG. 3 shows the setting of the duty ratio of the pulse ON width with respect to temperature information with the horizontal axis representing the junction temperature (Tj° C.) of the IGBT at −50° C. through 200° C. and the vertical axis representing the duty ratio (in the range from 5% through 95%) with respect to prescribed cycles of the pulse ON width corresponding to them. The frequency of a PWM signal used for outputting temperature information in FIG. 2 is usually set to several kHz, making it necessary to illustrate more precisely the transitions of duty ratios of a PWM signal used for outputting temperature information in order to express temperature information more accurately. However, a fine pulse ON width expressing a PWM signal, which requires too complicated an illustration, is omitted in FIG. 3.
Patent Document 1 below discloses a signal transmission circuit using an air-core insulation transformer that is separated into upper and lower arms, in which switching elements SWU and SWD are provided, switching elements SWU and SWD are driven by gate drivers IC8 and IC7 having a protection function and alarm output (alarm signals) of SU2 and SD2 and temperature information output of SU3 and SD3 are transmitted separately to the control unit side via insulation transformers TU2, TD2; TU3, TD3 from the side of a gate driver IC having a protection function.
Patent Document 2 below discloses an intelligent power module that provides as many insulation elements and terminals as there are signals. Specifically, an alarm signal propagation unit 11 includes a photocoupler (insulation element) and a temperature information propagation unit 12 also includes a photocoupler. Further, it is disclosed that an alarm signal and temperature information are output parallelly to the alarm signal propagation unit 11 and the temperature information propagation unit 12 from an intelligent power module 1.
As shown in FIG. 1, three photocouplers are required for a one-phase IGBT and the number of photocouplers increases for a larger IPM (Intelligent Power Module), also increasing the number of transmission terminals and reception terminals, leading to a wider space for mounting them and also leading to a higher cost. For example, a six-phase IPM having a three-phase inverter requires 18 photocouplers (3 (the number/phase) by 6 phases=18), leasing to a larger scale of device configuration due to increase in connection terminals for such photocouplers and also increasing the cost, which is problematic.
The conventional technique disclosed by Patent Document 1 above employs a configuration in which an alarm signal and temperature information are separately insulated by insulation transformers (insulation elements) to be output, increasing the number of insulation elements and also increasing the number of input terminals and output terminals so that reception is possible by using the insulation elements.
The conventional technique disclosed by Patent Document 2 above employs a configuration in which photocouplers are used as insulation elements and an alarm signal and temperature information are electrically insulated by separate photocouplers and are output, increasing the number of insulation elements and the number of input terminals and output terminals for transmitting and receiving signals via insulation elements, similarly to the Patent Document 1, which is problematic.
As described above, in a drive control method of the above conventional power semiconductor module, temperature information and an alarm signal are generated by separate circuits and the temperature information and the alarm signal are transmitted via different insulation elements such as photocouplers, increasing the number of insulation elements and also increasing the number of input terminals and output terminals for transmitting and receiving signals via insulation elements, which is problematic.    Patent Document 1: Japanese Laid-open Patent Publication No. 2008-277484 (FIG. 1)    Patent Document 2: Japanese Laid-open Patent Publication No. 07-115354 (FIG. 1 and FIG. 3)